Method of applying a ferromagnetic surface to a base utilizing iron carbonyl and oxygen



Dec. 29, 1959 K. SCHGLZEL 2,919,207

METHOD OF APPLYING A FERROMAGNETIC SURFACE TO A BASE UTILIZING IRONCARBONYL AND OXYGEN Filed Jan. 24, 1956 INVENTOR. KARL SCHCLZELATTORNEYS METHOD OF APPLYING A FERROMAGNETIC SURFAQE TO A BASE UTILIZKNGIRON CAR- BONYL AND OXYGEN Karl Schiilzel, Frankfurt am Main, Germany,assignor to Max 'Braun, Frankfurt am Main, Germany, a partnershipApplication January 24, 1956, Serial No. 561,124

2 Claims. (Cl. 117-106) The present invention relates to magneticrecording materials, such as those commonly used for the recording ofsound. In particular, the invention provides an I improved magneticrecording material and a novel method of applying extremely thinsubstantially homogenous ferromagnetic coatings to an appropriate basematerial which will generally be a non-magnetizable tape, disk, cylinderor structure of other suitable form.

Magnetic recording materials of this type are wellknown commodities andhave been made in the past by one of several techniques. Most commonly avery finely divided ferromagnetic material is combined with a bindermaterial which coats the base surface. Another technique consists inapplying a thin foil of the ferromagnetic material to the base surface.Use has also been made of electrodeposition, spray coating, coating byevaporation under vacuum, and coating by cathode sputtering. The betterof these processes are rather complicated and require costly apparatusand delicate controls, and those more easily carried out do notgenerally yield a high quality product. By the present invention, on theother hand, a ferrogmagnetic coating may very easily and accurately beapplied to produce a uniform recording material of very high quality. Ingeneral, the process consists in depositing the ferrogmagnetic coatingon the surface by thermally decomposing in situ the carbonyl of thedesired metal.

Carbonyl compounds are known for numerous metals which are eithermagnetizable or useful in forming mag netizable alloys such as iron,nickel, cobalt, and molybdenum, these metals being among the mostimportant constitutents of magnetizable substances. These compounds maybe converted to vapor form in which they are stable up to a temperatureat which they decompose to yield the metal. The present invention takesadvantage of this behavior, and is carried out by exposing the surfaceof the base material, at decomposition temperature, to the desiredcarbonyl compound in gaseous form. The carbonyl compound is thereupondecomposed at the surface of the base material to form a homogeneouscoating of the magnetizable metal.

The nature of the coating can easily be controlled by varying theconcentration and pressure of the vapors of carbonyl compound, and bycontrolling the time and temperature of exposure. Since theconcentration, and pressure over the entire area subject to exposure isquite uniform, and since time and temperature conditions are readilycontrollable, it will be appreciated that eXeremely consistent andaccurately controlled coatings may be formed Without the aid of bindermaterials.

Suitable carbonyl compounds are listed in Table I, which also givestheir boiling points and decomposition temperatures at atmosphericpressure. These compounds are defined herein as metallic carbonylcompounds of the Werner type, since they are formed by covalent (Werner)bonding of CO, alone or with other groups, to the metal.

2,919,207 Patented Dec. 29, 1959 Table I Vapor pressure Decom- Oarbonylcompound mm Hg at 0 position temp. 0

Iron pentacarbonyl, Fe(OO).; 160 Nickel carbonyl, Ni(00)4 60 Cobaltnitrosyl carbonly, 00(NO) (CO Cobalt carbonyl hydride, Co(OO)4H -33 Ironnitrosyl carbonyl, Fe(NO)2(O0)z 4 at 0 50 Iron carbonyl hydride,Fe(OO)4Hz 11 at -l0 33 Molybdenum carbonyl, M0(CO)0 2 3 at 55 From TableI it will be seen that numerous carbonyl compounds are available for usein this invention, including not only carbonyls, but also nitrosylcarbonyls and carbonyl hydrides. The carbonyls, e.g. iron pentacarbonyl,may be used alone or in admixture with other carbonyl compounds to givea ferromagnetic coating of controlled variable composition. Thus, thecoating may be iron or a mixture of iron and one or more other metals,e.g. cobalt, nickel and molybdenum.

Oxide coatings may also be formed by this invention by decomposing thecarbonyl, e.g. iron pentacarbonyl, on the base surface in the presenceof oxygen.

As base 'materials, any non-magnetizable material which is stable at thetemperatures encountered during deposition of the ferromagneticmaterial, and which may be formed with a smooth surface may be used.Particularly useful are paper and flexible organic plastic filmformingmaterials such as polyvinyl chloride, vinyl chloride-vinyl acetatecopolymers, vinylidene chloride, vinylidene chloride-vinyl chloridecopolymers, polyvinyl alcohol, polyethylene, polytetrafluoro-ethylene,polychlorotrifluoroethylene, polystyrene polyamides, rubberhydrochloride, vinyl nitrile rubber, regenerated cellulose, celluloseacetate, cellulose triacetate, cellulose acetate butyrate, cellulosenitrate, ethyl cellulose, polyethylene terephthalate, andpolymethylmethacrylate, to name but a few of the more common ones.Non-magnetizable metals, glass and numerous other materials having thegeneral properties described above are also entirely suitable as basematerials, provided that in each case a substance stable at thedecomposition temperature is used.

As a general procedure, the base material is heated to decompositiontemperature and exposed to the vapors of the carbonyl compound until acoating of the desired thickness has been deposited. The base materialmay be heated prior to the exposure and brought while still hot intocontact with the vapors, but a preferable practice is to heat the basematerial at its surface while it is in contact with the vapors. For thispurpose the base material may be heated by any one of numerouswell-known methods, such as by being passed in contact with a heatedsurface, by high frequency electromagnetic energy or by infraredradiation. Induction heating in the case of electrically conductivematerials may also be employed.

A preferred procedure as applied to the formation of an iron coating ona base tape is described below with reference to the accompanyingdrawing showing schematically suitable apparatus in which the inventionmay be practiced.

The apparatus consists in general of an elongated chamber 10 havingopposed slits 12 and 13 through which a tape to be coated may be run,and inlet and outlet conduits 14 and 15 by which an atmosphere of vaporsof a carbonyl compound may be maintained within the chamber. A heatingplaten 16 having a smooth upper surface over which the tape is passed ismounted within the chamber with power leads 17 for the heating element18 leading to a variable power source 20 by which the temperature of theplaten may be controlled. To prevent exposure of heated areas other thanthe top surface of the platen 16, insulation, as indicated at 21, may beprovided around the top surface.

The operation of the apparatus consists in feeding the tape 22 throughthe chamber and over the heating platen 16 while an atmosphere ofcarbonyl vapors is supplied to the chamber and while the temperature ofthe upper surface of the tape 22 is maintained above the decompositiontemperature of the carbonyl com pound.

In a typical operation for instance, an iron coating on a tape ofregenerated cellulose may be formed by supplying the chamber #10 withiron pentacarbonyl vapors under atmospheric pressure at a temperatureabove 103 C. (the boiling point of iron pentacarboxyl), preferably atabout 120 C., While heating the tape to between 160 and 200 C. A thinuniform homogeneous deposit of iron is thus formed by the reaction:

By introducing oxygen into the chamber in addition to the ironpentacarbonyl the iron may be deposited as ferromagnetic iron oxide,according to the reaction Although this invention has been describedwith reference to preferred embodiments, it is contemplated that obviousmodifications of its practice Will occur to those skilled in the art,and that such may be made without departing from the scope of theinvention.

Having thus disclosed this invention and described in detail preferredembodiments of it, I claim and desire to secure by Letters Patent:

1. The method of applying a ferromagnetic surface coating to anon-magnetizable base surface comprising heating said non-magnetizablebase surface, and contacting said surface with an atmosphere comprisingvapors of iron pentacarbonyl and oxygen, the temperature of the basesurface While in contact with said atmosphere being above thedecomposition temperature of the carbonyl compound, and the time ofcontact being such as to deposit a thin layer of ferromagnetic ironoxide suitable for magnetic recording on said base surface.

2. The method of applying a ferromagnetic surface coating to anon-magnetizable base surface comprising heating said non-magnetizablebase surface and contacting said surface with an atmosphere comprisingvapors of an iron carbonyl compound and oxygen, the temperature of thebase surface While in contact with said atmosphere being above thedecomposition temperature of the carbonyl compound, and the time ofcontact being such as to deposit a thin layer of ferromagnetic ironoxide suit-able for magnetic recording on said base surface.

References Cited in the file of this patent UNITED STATES PATENTS2,041,480 Oexmann May 19, 1936 2,616,165 Brennan Nov. 4, 1952 2,619,433Davis et a1. Nov. 25, 1952 2,671,034 Steinfeld Mar. 2, 1954 2,698,812Schladi-tz Jan. 4, 1955 2,784,115 Brinsmaid et a1. Mar. 5, 1957

1. THE METHOD OF APPLYING A FEROMAGNETIC SURFACE COATING TO ANON-MAGNETIZABLE BASE SURFACE COMPRISING HEATING SAID NON-MAGNETIZABLEBASE SURFACE, AND CONTACTING SAID SURFACE WITH AN ATMOSPHERE COMPRISINGVAPORS OF IRON PENTACARBONYLA AND OXYGEN, THE TEMPERATURE OF THE BASESURFACE WHILE IN CONTACT WITH SAID ATMOSPHERE BEING ABOVE THEDECOMPOSITION TEMPERATURE OF THE CARBONYL COMPOUND, AND THE TIME OFCONTACT BEING SUCH AS TO DEPOSIT A THIN LAYER OF FERROMAGNETIC IRONOXIDE SUITABLE FOR MAGNETIC RECORDING ON SAID BASE SURFACE.